Codigestion of pig slurry and organic wastes from food industry

PROCEEDINGS OF THE II INTERNATIONAL SYMPOSIUM ON ANAEROBIC DIGESTION OF SOLID WASTE. BARCELONA. JUNIO 1999. PAG. 192-195. CODIGESTION OF PIG SLURRY AND ORGANIC WASTES FROM FOOD INDUSTRY Elena Campos, Jo di Pala si and Xa ie Flo a s Depa men o En i onmen and Soil Science, Uni e si y o Lleida. Ro i a Rou e, 177. 25198 Lleida, Spain. ABSTRACT Anae obic diges ion o pig slu y can be a good op ion o ge a highe alue o hese was es. Al hough he mophilic anae obic diges ion is mo e e icien han mesophilic anae obic diges ion, i p esen s some limi a ions, like less s abili y and an inc eased e ec o some inhibi o s. The main inhibi o o pig slu ies is ee ammonia. In o de o imp o e he me hane p oduc ion, some mix u es o slu y and o ganic was es om ood indus y we e es ed, like was es om ui and oli e oil e ine y indus ies (pea was e and oil bleaching ea h). A ba ch expe imen was ca ied ou , in o de o de e mine he maximum po en ial o me hane p oduc ion and biodeg adabili y o hese was es. The expe imen was de eloped in mesophilic and he mophilic anges (35º and 55º). The mesophilic esul s we e be e han he he mophilic ones, showing a la ge inhibi ion by ammonia in he he mophilic ange. In bo h empe a u e anges, he me hane p oduc ion was imp o ed by addi ion o a co-subs a e. The highe me hane p oduc ion was ob ained om he codiges ion o slu y and oil bleaching ea h (95% and 5% espec i ely). The me hane yield was 344 mL CH4/g VSini ial, which is 2.4 imes he me hane yield o slu y (144.0 mL CH4/g VSini ial). KEYWORDS: Anae obic diges ion; codiges ion; ammonia inhibi ion; o ganic indus ial was es; pig slu y; empe a u e. INTRODUCTION In Ca alonia he e a e mo e han i e million pigs, p oducing mo e han 30.000 m3/day o was es. The anae obic diges ion can be a good op ion o ge a highe alue o hese was es. The mophilic anae obic diges ion has some heo e ical ad an ages o e mesophilic, like a be e sani a ion o e luen s, as e p ocess a es and bigge me hane yield. Howe e , he slu y p esen s a e y high concen a ion o ammonia, which has been desc ibed as a e y impo an inhibi o o anae obic p ocess. F ee ammonia is he ac i e componen causing ammonia inhibi ion (Angelidaki e al., 1993), and i s concen a ion depends on he o al ammonia, pH and empe a u e. The inhibi o y concen a ion depends on he mic o-o ganisms adap a ion phenomena (Van Velsen e al., 1979; Kos e , 1986; Hansen e al., 1998). So, a wide a ie y o inhibi o y alues a e ound in he li e a u e, i.e. 80 mg N-NH3/L (Kos e , 1986), 700 mg N-NH3/L (Angelidaki e al., 1993) o 1100 mg N-NH3/L (Hansen e al.1998). By codiges ion o di e en ypes o was es, such as manu e, household solid was e and o ganic indus ial was e, a highe gas yield can be ob ained om biogas eac o s. Indus ial was es a e mo e easily deg adable and ha e a highe gas po en ial han manu e, a ying om 30 o 500 m3/ on (Ah ing e al., 1992; Angelidaki e al., 1997). Slu y can be an excellen basic subs a e o he codiges ion, because i has a high wa e con en s, a high bu e ing capaci y and a wide a ie y o needed nu ien s o anae obic bac e ia. (Angelidaki e al., 1997). P e ious expe ience o codiges ion o slu y and sewage sludge, wi h sa is ac o y esul s, has been epo ed (Flo a s e al., 1999). Codiges ion o manu e and oil bleaching ea h (OBE) has p o ided e y good esul s in Denma k (Ah ing e al., 1992), due o he high lipids con en o his kind o was es, ha p o ides a high po en ial o biogas p oduc ion (Ah ing e al., 1992). Howe e , an excess o lipids can cause inhibi ion (Hanaki e al., 1981; Ah ing e al.,1992). O he in e es ing indus ial was es a e hose p oduced in ui juice ac o ies. The main p oblem associa ed wi h diges ion o ligno-cellulosic was es is he main enance o s able pH, which is associa ed wi h i s poo bu e ing capaci y and ola ile a y acids accumula ion. Combina ion wi h ano he was e wi h high bu e ing capaci y can be a good way o diges i (Banks e al., 1998). Bo h ypes o was es (OBE and pea was e) a e p oduced in la ge quan i y in he a ea o Lleida (Ca alonia, Spain), and he objec i e o he p esen wo k is o analyse he pe o mance o i s codiges ion wi h pig slu y, using ba ch diges ion es s. MATERIAL AND METHODS The ba ch eac o s we e 120 mL glass ials, illed wi h 50 g. o sample and 5 g. o inoculum, ini ially bubbled wi h N2/CO2 gas mix u e o ai displacemen , igh ly closed wi h ubbe aps, placed in incuba o s held a 35ºC (mesophilic es ) and 55ºC ( he mophilic es ), and ollowed o 75 days. Fi e epe i ions we e in ol ed o e e y ea men and e e y empe a u e. Duncan’s mul iple s a is ical es was applied o gas p oduc ion compa ison among ea men s and empe a u es. The inoculum p oceeded om an anae obic diges e ea ing pig slu y since 1983, in he mesophilic ange. The pig slu y used came om a a ening pig a m nea Lleida. The pea was e came om a ui juice ac o y, close o Lleida. The OBE was e came om an oli e oil bleaching and il e ing ac o y. The expe imen al design consis ed o ele en ea men s and a blank un, pe o med a 35ºC and 55ºC empe a u es. Table 1 shows p opo ions used o each co-subs a e and subs a e composi ion o each ea men . TABLE 1. SUBSTRATE COMPOSITION FOR EACH TREATMENT T ea men Slu y % Pea Was e % OBE % Wa e % TS (1) VS (1) COD (2) TKN (3) NH4 + (3) pH To al Alk (4) VFA Alk (5) Alk. Ra e T1 100 - - 0 7.92 5.87 82.50 5.06 3.43 8.06 10.55 3.66 0.29 T2 95 - - 5 7.52 5.58 78.37 4.82 3.28 7.96 10.05 3.30 0.27 T3 87.5 - - 12.5 6.93 5.14 72.18 4.44 2.97 8.03 8.98 3.09 0.29 T4 80 - - 20 6.33 4.69 66.00 4.05 2.70 7.95 8.20 2.88 0.29 T5 95 5 - - 9.29 7.29 102.4 4.91 3.21 7.55 9.75 3.66 0.31 T6 87.5 12.5 - - 11.35 9.45 132.3 4.98 3.01 7.25 8.73 3.54 0.34 T7 80 20 - - 13.41 11.63 162.1 4.66 2.71 6.88 7.58 3.39 0.37 T8 - 20 - 80 7.08 6.98 96.14 0.89 0.08 3.45 0.00 0.00 - T9 95 - 5 - 12.40 7.54 136.9 4.76 3.20 7.69 9.50 3.75 0.33 T10 87.5 - 12.5 - 19.13 10.09 218.5 4.48 3.04 7.33 8.10 3.66 0.38 T11 - - 12.5 87.5 12.2 4.94 58.54 0.38 0.04 6.93 0.95 0.90 0.79 (1)To al and ola ile solids a e exp essed as % (w/w); (2) Chemical Oxygen Demand in g O2/Kg; (3) To al Kjeldahl Ni ogen and o al ammonia a e exp essed as g N/Kg; (4) To al alkalini y is exp essed as g CaCO3/L; (5) Vola ile a y acids alkalini y is exp essed as g AcH/L. Analy ical p ocedu es. Gas analysis (N2, CH4, CO2) we e ca ied ou by gas ch oma og aphy using a The moques 8000 ch oma og aph wi h a TCD and a packed s eel column Po apak N. To al and ola ile solids, COD, pH, alkalini y and Kjeldahl and ammonia ni ogen we e de e mined acco ding o S anda d Me hods (APHA, 1995). F ee ammonia concen a ion was calcula ed om he equilib ium ela ionship. RESULTS AND DISCUSSION Accumula ed me hane p oduc ion and yields ob ained a 75 days ba ch es a e p esen ed in Table 2, wi h he esul s o he Duncan es . Resul s in mesophilic expe imen . Non s a is ically signi ican di e ences we e ob ained among he di e en slu y dilu ions es ed ( ea men s T1-T4), showing non-inhibi ion e ec by ammonia o his empe a u e. Al hough he high o al ammonia concen a ion (2.7-3.4 g N-NH4/L), he ee ammonia concen a ion p esen s a low alue a he beginning o he diges ion. The e ec o slu y/pea mix u e was no signi ican o me hane ( ea men s T5-T8). Fo T7 ea men (20% o pea was e), he p ocess ailed, p obably due o a less bu e ing capaci y and a highe ib e con en s. Diges ion o pea was e (T8) couldn’ de elop due o a low pH and bu e ing capaci y. Codiges ion o slu y and OBE ( ea men s T9-T10) showed a e y good beha iou a 35ºC, p esen ing a s a is ically signi ican highe me hane p oduc ion han hose ob ained o he o he ea men s. The T10 p ocess showed a lag phase, p obably due o a sligh inhibi ion by long chain a y acids. The lipid con en s in his mix u e was 35.7 g/L, highe han alues epo ed by o he au ho s (Ah ing e al., 1992; Hanaki e al., 1981). TABLE 2. METHANE PRODUCTION AND YIELD BY TREATMENT AND TEMPERATURE, AT 75 DAYS BATCH TEST Me hane P oduc ion (mL CH4) Me hane Yield (mL CH4/gSVini) Me hane Yield (mL CH4/gSVini) 55ºC 35ºC 55ºC 35ºC Di e ences due o empe a u e T1 192.6 de 439.8 c 63.1 c 144.0 b 80.9* T2 199.1 de 425.1 c 70.0 cd 144.0 b 74.0* T3 246.2 e 365.8 c 90.8 de 134.8 b 44.0* T4 293.4 367.3 c 114.6 143.6 b 29.0* T5 419.1 g 534.0 c 110.7 e 141.0 b 30.3* T6 518.0 h 828.4 d 107.4 e 171.6 b 64.2* T7 535.3 h 188.4 b 88.1 de 31.0 a -57.1* T8 0.0 a 0.0 a 0.0 a 0.0 a - T9 6.8 ab 1289.0 1.8 a 343.9 d 342.1* T10 136.5 cd 1050.1 e 26.9 b 206.6 c 179.7* T11 77.3 bc 9.8 a 29.7 b 3.8 a - Duncan’s mul iple es wi h a 95% con idence le el: Di e en le e means signi ican di e ences among he means, by columns ( o each empe a u e); (*) means signi ican di e ences be ween empe a u es o each ea men . Resul s in he mophilic expe imen . Fo slu y dilu ion ea men s, he highes me hane p oduc ion was ob ained in he T4 ea men (20% o wa e ). In hese expe imen s, me hane yield and ini ial ee ammonia concen a ion a e e y well co ela ed, as can be shown in Figu e 1, indica ing a signi ican inhibi o y ammonia e ec . Fo slu y/pea mix u es, he highes yield alue was 110.7 mL CH4/g VS o T5 ea men , which is smalle han T4 ea men , bu no s a is ically di e en . Taking in o accoun ha he T5 ea men has highe ini ial ammonia concen a ion han he T4, i can be said ha he main e ec o pea was e is he addi ion o o ganic ma e . Co-diges ion o slu y and OBE p esen ed low gas p oduc ion, indica ing inhibi ion by ammonia and LCFA. All ea men s p esen signi ican di e ences, a 95% con idence le els, be ween mesophilic and he mophilic anges. Inhibi ion by ee ammonia concen a ion a he mophilic ange, inc easing o 1000 mg N-NH3/L du ing he expe imen , could be he main e ec . Taking in o accoun some p e ious good expe iences wi h highe le els o ammonia con en s (Hansen e al., 1998), he impo ance o he adap a ion o biomass used as inoculum mus be ema ked. Figu e 2. Co ela ion be ween me hane yield and ee ammonia concen a ion, a 55ºC CONCLUSIONS Codiges ion o slu y wi h o he subs a es could be a e y good op ion o inc ease he me hane p oduc ion. Codiges ion wi h OBE showed a e y good beha iou a mesophilic ange, wi h a me hane yield 2.4 imes bigge han o slu y diges ion. The main e ec o pea was e addi ion was inc ease o o ganic ma e . In gene al he mesophilic ange showed a be e beha iou han he he mophilic one, showing a clea inhibi ion by ee ammonia. The p e ious adap a ion o inoculum is basic o p ocess pe o mance. ACKNOWLEDGMENTS This esea ch has been suppo ed by he Lleida Council (Pae ia), and by a g an om CIRIT (Gene ali a o Ca alunya). REFERENCES Ah ing, B., Angelidaki, I., Johansen, K.(1992).Anae obic ea men o manu e oge he wi h indus ial was e. Wa . Sci. 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Hansen, K., Angelidaki, I., Ah ing, B.(1998). Anae obic diges ion o swine manu e: Inhibi ion by ammonia. Wa e Resea ch, 32 (1), 5-12. Kos e , I.W. (1986). Cha ac e is ics o he pH-in luenced adap a ion o me hanogenic sludge o ammonium oxici y. J- Chem. Tech. Bio ech 36, 445-455. Van Velsen (1979). Adap a ion o Me hanogenic sludge o high ammonia-ni ogen concen a ions. Wa e Resea ch, 13, 995-999 CH4/VSi = -0.0636*[N-NH3] + 72.962 R2 = 0.7777 CH4/VSi = -0.2889*[N-NH3] + 341.56 R2 = 0.8573 0 20 40 60 80 100 120 140 700 750 800 850 900 950 1000 N-NH3 (mg N/L) mL CH4/g VSi Day 15 Day 75